1. Field of the Invention
The present invention relates to a hydroformylation process of cyclic olefins in the presence of a metal catalyst, and in particular relates to the separation of the desired products from the metal catalyst by phase separation.
2. Description of the Related Art
It is known in the art that compared to a heterogeneous catalyst, the homogeneous catalyst has advantages such as high reactivity, high selectivity, and a relatively milder reaction condition. However, many homogeneous catalyst systems cannot be commercially applied mainly due to difficulties in separating, recovering, and reusing the homogeneous catalysts, as it is well known.
It is known in the art that distillation is one of the favorable methods for the separation of catalysts and products. If the volatility of the product is low, the temperature required to separate the product by distillation should be higher. Most homogeneous catalysts, however, are thermal sensitive, such that the homogeneous catalyst may decompose during higher distillation temperatures and fail to be recovered for reuse. Other methods for recovering the homogeneous catalyst, e.g. chromatography, are inefficient. Accordingly, an effective and low cost separation process is critical for development of the homogeneous catalyst.
Hydroformylation of olefins with carbon monoxide (hereinafter CO) and hydrogen (hereinafter H2) to form aldehydes is an important homogeneous catalytic reaction. The catalysts used for the hydroformylation of olefins are usually rhodium or cobalt catalysts, especially the rhodium catalysts due to their high reactivity and selectivity. Although rhodium catalysts have higher reactivity, their cost is much higher than the cobalt catalysts. The effective recovery and reuse of the rhodium catalysts determines their realization in the industry. If the volatility of the hydroformylation products (less than C5) is relatively high, the low temperature distillation method can be used to separate the products and the catalysts without significantly decomposing the catalysts. On the other hand, if the volatility of the hydroformylation products is low, the abovementioned distillation method for separation is unfavorable, due to the decomposition of the catalyst at higher temperatures such that the catalyst cannot be recovered and reused, thus increasing costs.
As described above, the products from hydroformylation of cyclic olefins have a higher boiling point. If the product and catalyst are separated by vacuum distillation, a higher distillation temperature is needed, thereby decomposing the rhodium catalyst. In WO 93/02024, a mixture of first alcohol having 1 to 3 carbon atoms and water is reported to be used as an extraction solution to separate the rhodium catalyst and high boiling-point aldehydes from hydroformylation. The efficiency of this method is, however, not good, and a better method for the efficient separation of the hydroformylation products and catalyst is still needed.